1. Field of the Invention
The present invention relates to an optical deflector, an optical scanner that includes the optical deflector, and an image forming apparatus that includes the optical scanner.
2. Description of the Related Art
In the field of image forming apparatuses, such as copiers, facsimile machines, and printers that form images by converting electric data into optical data, forming based on the optical data an electrostatic latent image on an image carrier by an optical scanner, and developing the electrostatic latent image into a toner image, the high-speed and high-density image formation is required in addition to the full-color image formation.
To satisfy such needs, some manufacturers increases the number of polygon mirrors that are used in an optical deflector of the optical scanner, or increases rotation speed of the optical deflector. However, the increase in the number of the polygon mirrors or the increase in the rotation speed disadvantageously causes increase in vibration and noise, which are due to eccentricity of the polygon mirrors, wind roar, which is due to friction with ambient air, and temperature.
To solve the problems, Japanese Patent Application Laid-open No. 2005-092129 discloses an optical deflector, which is used in a full-color image forming apparatus, for achieving high-speed and high-density scanning. The optical deflector includes a plurality of small-size polygon mirrors tightly connected to each other. Because the polygon mirrors are tightly connected to each other, the optical deflector generates less noise even during high-speed rotation, and the polygon mirrors scarcely deviate from each other due to acceleration and temperature change.
Even in the optical deflector disclosed in Japanese Patent Application Laid-open No. 2005-092129, strong vibration may occur due to resonance when the rotation frequency increases close to a natural frequency of the optical deflector as the rotation speed increases. The strong vibration may cause deviation of a deflected beam and decrease quality of an output image. To solve the problem, Japanese Patent Application Laid-open No. 2005-010260 and Japanese Patent Application Laid-open No. 2001-065560 disclose technologies for suppressing the vibration by using a dynamic absorber.
However, such technologies increase the cost for the additional parts. Moreover, because an enough-large dynamic absorber cannot be used, the vibration is not suppressed to a large extent.